The invention concerns a method and a system for controlling the pressure of a high-pressure fuel pump for feeding an internal combustion engine.
More precisely, the invention relates to the control of the pressure in a high-pressure fuel circuit for feeding, through at least one injector, an internal combustion engine, in particular with direct injection, especially with externally supplied ignition, but not excluding compression (diesel type) ignition.
In a system according to the invention, the internal combustion engine mechanically drives a high-pressure pump of the type with at least one reciprocating piston in a corresponding cylinder, the mechanical driving of the piston being for example being performed by a camshaft driven by the engine or belonging to the latter, and the high-pressure pump discharging into the high-pressure circuit, which is the type without a continuous return of the fuel from the downstream end to the upstream end of the pump, the fuel pressure in the high-pressure circuit being measured by at least one pressure sensor, and the pump being equipped, for each piston, with an on-off solenoid valve for controlling the fuel supply of the corresponding pump cylinder.
In known systems of this type, which pressurize the fuel using a high-pressure pump mechanically driven by the internal combustion engine fed by the pump, wherein the quantity of fuel delivered per pump cycle for each piston is controlled by an on-off solenoid inlet valve, which determines the volumetric efficiency of the pump by controlling the circuit that supplies fuel to the pump, it is known to try to establish, in the high-pressure circuit between the pump and the engine, a fuel pressure equal to a target pressure, determined as a function of operating parameters and/or conditions of the internal combustion engine, by performing a direct control, acting directly on the quantity of fuel delivered by the pump so as to increase, or respectively decrease, this quantity per pump cycle depending on whether the fuel pressure measured in the high-pressure circuit by the pressure sensor is lower than, or respectively higher than, the target pressure.
The drawback of these known pressurization systems is that they provide a simplified control that does not take into account the operating modes of the various components of the system, and in particular the high-pressure fuel circuits.
The basic problem of the invention is to eliminate this drawback and to offer a pressure control method and system that provides more precise control by establishing a fuel pressure approximately equal to a target pressure by acting on a control parameter that is not directly linked to the quantity to be controlled, i.e., the fuel pressure in the high-pressure circuit, the control parameter in this case being the control sequence of the solenoid valve at the inlet of each cylinder of the high-pressure pump.
To this end, the pressure control method according to the invention of the above-mentioned type is characterized in that it includes the step that consists of controlling the fuel pressure by driving the solenoid valve so that the fuel mass delivered by said pump into said high-pressure circuit is equal to the algebraic sum of a fuel mass to be injected into the internal combustion engine (and known by an engine control unit that controls at least the fuel injection into the engine), and of a required fuel mass, or a quantity determined from said required mass, for at least partially correcting the pressure difference between the fuel pressure measured in the high-pressure circuit by means of said pressure sensor and a target pressure desired in said high-pressure circuit.
Thus, the fuel pressure in the high-pressure circuit is controlled, particularly for direct injection, by using a solenoid valve to control the supply of fuel to the high-pressure pump, this solenoid valve making it possible to adjust the quantity of fuel delivered by the pump in the high-pressure circuit, and thus to adjust the fuel pressure in the circuit so as to bring it in line with the target pressure.
Advantageously, said required fuel mass for at least partially correcting the difference between the measured and target pressures is determined by means of at least one relation between the mass or mass variation of the fuel, and the pressure or pressure variation of the fuel in said high-pressure circuit, so as to take into account the operating mode of the high-pressure circuit, and in particular its behavior and that of the fuel that the circuit contains under the operating conditions of the circuit, considering the quantities of fuel delivered by the pump into this circuit.
Advantageously, this relation between the mass or mass variation and the pressure or pressure variation of the fuel in the high-pressure circuit is determined by taking into account at least one of the operating parameters, such as the measured pressure and the temperature of the fuel, and/or the compressibility law of the fuel used, and/or at least one of the geometric parameters of the high-pressure circuit, and/or at least one of the mechanical and/or physical properties of the materials of the elements constituting said high-pressure circuit.
In order to adapt the quality of the control in terms of speed, stability and precision, the control method advantageously also includes a step that consists of weighting the required fuel mass for correcting the difference between the measured and target pressures with a correction of the proportional-integral-derived type, this correction being performed for example by an algorithm of a well-known type.
After having calculated the fuel mass that the pump should deliver, the method of the invention also provides for a determination of the moments of operation of the solenoid valve, taking into account the operation of the pump and the operation of the solenoid valve. For this purpose, as concerns the operation of the pump, the method of the invention advantageously also includes a step that consists of controlling the solenoid valve, taking into account at least one relation between the delivery rate of the pump and the angular position of the engine, which mechanically drives it, during the closed periods of said solenoid valve. More generally, the method of the invention takes into account a relation that indicates the quantity of fuel delivered by the pump to the high-pressure circuit as a function of the sequencing of the opening and closing of the solenoid valve located in the supply circuit of said pump.
For better precision, this relation expressing the delivery rate of the pump advantageously takes into account at least one operating parameter such as the fuel pressure, the rotation speed and/or the operating temperature of the pump.
As concerns the behavior of the solenoid valve, the method of the invention advantageously also includes a step consisting of controlling said solenoid valve, taking into account at least one relation between the delay in the actual openings and closings of the solenoid valve relative to the electrical commands for controlling the opening and the closing, and also at least one of the operating parameters and conditions of said solenoid valve, and preferably at least one parameter related to the fuel.
Preferably, in order to obtain good precision, this relation related to the delay of the solenoid valve takes into account at least one of the parameters that include the supply voltage and the operating temperature of the solenoid valve, as well as the difference in fuel pressure between the inlet and the outlet of said solenoid valve.
The invention also relates to a system for controlling the pressure in a high-pressure fuel circuit for feeding, through at least one injector, an internal combustion engine, in particular with direct injection, and especially with externally supplied ignition, a system wherein said engine mechanically drives a high-pressure pump of the type with at least one reciprocating piston in a corresponding cylinder, said pump discharging into said high-pressure circuit, which is the type without a continuous return of the fuel from the downstream end to the upstream end of said pump, and wherein the fuel pressure is measured by at least one pressure sensor of the system, said pump being equipped, for each piston, with an on-off solenoid valve for controlling the fuel supply of the corresponding pump cylinder, and according to the invention, this system is characterized in that it includes at least one electronic pressure control unit, in connection with or integrated into an electronic engine control unit, which controls the injection and, if necessary, the ignition of the engine, and determines, in particular, the fuel mass to be injected into the engine, said electronic pressure control unit [operating the solenoid valve in order to control the feeding of said cylinder of the pump and] including computing means and storage means and being equipped to implement the method according to the invention as defined above, and the electronic pressure control unit comprising at least one module for determining the relation, possibly weighted, between the mass or mass variation and respectively the pressure or pressure variation of the fuel in the high-pressure circuit, at least one module for determining the target pressure desired in said high-pressure circuit as a function of operating parameters and/or conditions of the engine, at least one module for determining the fuel mass to be delivered by the pump into the high-pressure circuit, as a function of a signal of the fuel mass to be injected into the engine and received by the engine control unit, and of the fuel mass for compensating the pressure difference between the pressure measured by the pressure sensor and the target pressure, at least one module for determining the delay of said solenoid valve, and at least one module for determining the delivery rate of the pump as a function of the angular position of the engine and of the sequencing of the opening and closing of said solenoid valve.